Oxidation of acrolein and methacrolein with a molybdenum polyvalent metal oxygen catalyst

ABSTRACT

The invention relates to a process for the production of acrylic acid or methacrylic acid by the vapor phase oxidation of acrolein or methacrolein with molecular oxygen in the presence of an oxidation catalyst consisting essentially of (1) a mixture of an oxide of molybdenum and an oxide of a polyvalent metal other than cobalt or (2) a compound of molybdenum, oxygen and a polyvalent metal other than cobalt.

United States Patent [191 Bethell et al.

[111 E Re. 28,593

1 Reissued Oct. 28, 1975 OXIDATION OF ACROLEIN AND METHACROLEIN WITH AMOLYBDENUM POLYVALENT METAL OXYGEN CATALYST [75] Inventors: James RobertBethell, Ewell,

England; Edward James Gasson, Dollar, Scotland; David James Hadley,Tadworth, England; Roderick Frank Neale, Midlothian, Scotland [731Assignee: BP Chemicals International Limited,

London, England [22] Filed: Dec. 27, 1973 [21] App]. No.: 428,751

Related US. Patent Documents Reissue of:

[64] Patent No.: 3,435,069

Issued: Mar. 25, 1969 Appl. No.: 493,561 Filed: Oct. 6, 1965 US.Applications: [63] Continuation-impart of Ser. No. 100,492, April 4,

1961, abandoned.

[30] Foreign Application Priority Data Apr. 14. 1960 United Kingdom11310/60 May 12, 1960 United Kingdom... 16750/60 Aug. 4, 1960 UnitedKingdom 26993/60 [52] US. Cl 260/530 N; 260/531 R; 260/533 N; 252/455 R;252/456; 252/458; 252/459; 252/464; 252/465; 252/467; 252/469; 252/470Primary ExaminerLorraine A. Weinberger Assistant Examiner-Richard D.Kelly Attorney, Agent, or FirmBrooks Haidt Haffner &

DeLahunty [57] ABSTRACT The invention relates to a process for theproduction of acrylic acid or methacrylic acid by the vapor phaseoxidation of acrolein or methacrolein with molecular oxygen in thepresence of an oxidation catalyst consisting essentially of(l) a mixtureof an oxide of molybdenum and an oxide ofa polyvalent metal other thancobalt or (2) a compound of molybdenum, oxygen and a polyvalent metalother than cobalt.

17 Claims, No Drawings OXIDATION OF ACROLEIN AND METHACROLEIN WITH AMOLYBDENUM POLYVALENT METAL OXYGEN CATALYST Matter enclosed in heavybrackets I: appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

This application is a continuation-in-part of our previously filed,copending application Ser. No. 100,492, filed Apr. 4, l96l nowabandoned.

The present invention relates to the production of unsaturated aliphaticacids and particularly to the production of acrylic and methacrylicacids.

In copending application Ser. No. 4,22l filed Jan. 25, 1960 is describedthe process for the production of acrylic acid or methacrylic acid whichcomprises reacting at an elevated temperature in the vapour phaseacrolein or methacrolein, or a compound which gives rise to acrolein ormethacrolein under the reaction conditions, with molecular oxygen overan oxidation catalyst comprising (i) a mixture of the oxides ofmolybdenum and cobalt, and/or (ii) a compound of molybdenum, cobalt, andoxygen, such as cobalt molybdate.

According to the present invention the process for the production ofacrylic acid or methacrylic acid comprises reacting at an elevatedtemperature in the vapour phase acrolein or methacrolein, or a compoundwhich gives rise to acrolein or methacrolein under the reactionconditions, with molecular oxygen over an oxidation catalyst comprising(i) a mixture of the oxides of molybdenum and a polyvalent metal ormetals other than cobalt, and/or (ii) a compound of molybdenum, oxygenand a polyvalent metal or metals other than cobalt.

By the term polyvalent" is meant having more than one valency state.

The preferred starting material is acrolein, but compounds giving riseto acrolein under the reaction conditions, such as propylene or allylalcohol, and mixtures of propylene and acrolein, may also be used.Methacrolein may also be used as starting material in the process, andis converted to methacrylic acid. When the starting material is anolefine such as propylene, the reaction product consists of theunsaturated acid with the corresponding unsaturated aliphatic aldehyde.Thus propylene is converted into a mixture of acrylic acid and acrolein.

The catalysts used in the process must include molybdenum, oxygen and apolyvalent metal or metals and may be regarded either as mixtures ofmolybdenum oxides with oxides of the polyvalent metal or metals, or asoxygen-containing compounds of molybdenum and the polyvalent metal ormetals, such as antimony molybdate. Under the reaction conditions thecatalyst may be present in both forms. in a preferred embodiment thecatalyst should consist of the mixture of oxides and/or compound orcompounds only without any additional catalytic material. Polyvalentmetals may be for example vanadium, iron, cerium, [titanium,] antimony,tin, and tungsten [and bismuth] The use of antimony and tin molybdate isparticularly preferred. The catalyst may if desired be deposited on asupport such as alumina or silica. The catalyst may be convenientlyprepared, for example, by precipitation from mixed solutions of salts ofthe polyvalent metal or metals with molybdenum salts. For example, byadding an aqueous solution of an antimony salt to an aqueous solution orsuspension of molybdic acid or a molybdic acid salt, and recovering theresulting precipitate; or adding the metal to boiling dilute nitric acidto form a white precipitate, filtering and washing the precipitate withwater and mixing it with molybdic oxide and water to form a slurry whichis then dried and formed into pellets. Alternatively the catalyst may beprepared by mere admixture of the desired polyvalent metal oxide oroxides with oxides of molybdenum. The catalyst is suitably given a heattreatment before use, for instance to a temperature between 500 and l300C.

The atom ratio of polyvalent metal to molybdenum in the catalyst mayvary within moderately wide limits. It may be as high as 20:1 or as lowas 1:6.5, and these ratios will apply irrespective of the specificpolyvalent metal employed. These ratios are determined by the followingmathematical calculation:

NmWm

Mm I

In the expression:

Nm=number of atoms of polyvalent metal present in starting compound ofoxide Wm=starting weight of such compound or oxide Mm=the molecularweight of such compound or oxide NMb, WMb and MM!) are the correspondingvalues for molybdenum.

The reaction may be carried out in any suitable manner, for instance asa fixed bed process, or as a fluidised bed process.

The proportion of aldehyde or compound producing aldehyde under reactionconditions, e.g. olefine, in the feed may vary within wide limits, forexample between I and 20% by volume, and preferably between about 2 and10% by volume.

The concentration of oxygen in the feed may also vary within moderatelywide limits, for example between l and 20% by volume and preferablybetween 2 and 15% by volume. The oxygen may be diluted with inert gases,and may be, for example, supplied as air.

it is preferred to carry out the reaction in the presence, as diluent,of a gas which is substantially inert under the conditions of reaction,for example, nitrogen, propane, butane, isobutane, carbon dioxide orsteam. it is preferred to use steam or nitrogen or mixtures thereof. Theconcentration of the steam may vary within wide limits, for instancebetween 20 and 60% by volume of the feed.

The reaction is carried out at an elevated temperature, preferablybetween 300 C. and 500 C.

The contact time may be, for example, in the range l30 seconds.

The unsaturated acid may be removed free from acrolein from the reactiongas mixture in any suitable manner, for example by extraction with asolvent such as water followed by fractional distillation of theresulting aqueous solution.

The process of the invention is further illustrated by the followingexamples. In the examples, parts are by weight and parts by volume bearthe same relation to each other as do grams to milliliters.

[Example 1] [A hot solution of 97 parts by weight of bismuth nitrate indilute nitric acid (35 parts by weight of nitric acid specific gravity1.42 mixed with 225 parts by weight of water) was added with stirring toa warm solution of 53 parts by weight of ammonium molybdate in 50 partsby weight of water containing a little ammonia. The mixture was boiledand the precipitate filtered off, washed with water and dried. The drymass was broken down and the powder mixed with 2% of graphite andpelleted, the pellets then being heated at 540C. for 16 hours. Thebismuth to molybdenum atomic ratio in the catalyst is 1:15.

A gaseous mixture of 9.5% by volume of acrolein, 10.6% by volume ofoxygen, 51.2% by volume of nitrogen, and 28.7% by volume of steam waspassed over the catalyst in a reactor maintained at 400 C., the contacttime being 3.2 seconds.

Of the total acrolein fed to the reactor, 8.7% was converted to acrylicacid, 7.5% to carbon dioxide and 71.3% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 30.3%.]

[ Example 2 [A solution of 5 parts of bismuth nitrate in dilute nitricacid (4 parts of nitric acid 8.6. 1.42 in 9 parts of water) was added toa warm solution of 12 parts of ammonium molybdate in 24 parts by water.15 parts of 8-16 mesh B.S.S. kieselguhr was stirred into the pale yellowsludge, and the resulting solid was heated initially at 260 C. for 6hours and then at 510 C. for 16 hours; the resulting catalyst was sievedto 8-16 mesh B.S.S. The bismuth to molybdenum atomic ratio in thecatalyst is 1:6.5.

A gaseous mixture of 7.9% by volume of methacrolein, l 1.8% by volume ofoxygen, 44% by volume of nitrogen and 36.3% by volume of steam waspassed over the catalyst maintained in a reactor at 367 C., the contacttime being 4.0 seconds.

Of the methacrolein fed to the reactor 4.1% was converted to methacrylicacid, 1.9% to carbon dioxide and 84.1% was recovered unchanged.

The yield of methacrylic acid based on methacrolein consumed was 25.8%.]

Example 3 1 50 parts by weight of tungstic acid was stirred with asolution of ammonia (66 parts by weight of 0.880 ammonia mixed with 75parts by weight of water) until no more tungstic acid dissolved. Themixture was filtered, and to the filtrate a solution of 35 parts byweight of ammonium molybdate in 50 parts by weight of water was added;dilute hydrochloric acid was then added to this mixture with stirringuntil precipitation was complete. The precipitate was filtered off.washed with water and dried, the dry mass being broken down to granulesof 8 to 16 mesh B.S.S. The tungsten to molybdenum atomic ratio in thecatalyst is 1:0.98.

A gaseous mixture of 10.4% by volume of acrolein, 10.2% by volume ofoxygen, 49.6% by volume of nitrogen, and 29.7% by volume of steam waspassed over the catalyst maintained in a reactor at 350 C., the contacttime being 4.0 seconds.

Of the acrolein fed to the reactor 46.1% was converted to acrylic acid,11.2% to carbon dioxide, and 18.6% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 56.6%.

I: Example 4 [144 parts by weight of molybdic oxide and 79.9 parts byweight of titanium dioxide were mixed together with a little water toform a slurry, and the mixture then dried. The dry catalyst mass wasbroken down to pass a 30 mesh B.S.S. sieve, mixed with 2% of graphiteand pelleted. The catalyst pellets were then heat treated at 600 C. for16 hours. The titanium to molybdenum atomic ratio in the catalyst is1:1.

A gaseous mixture of 10.2% by volume acrolein, 10.0% by volume ofoxygen. 50.4% by volume of nitrogen and 29.4% by volume of steam waspassed over the catalyst maintained in a reactor at 400 C. the contacttime being 4.0 seconds.

Of the acrolein fed to the reactor 24.6% was converted to acrylic acid,5.7% to carbon dioxide, and 51.1% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 50.3%.]

Example [5 1 2 A solution of 132.4 parts by weight of ammonium molybdatein 500 parts of water was added dropwise to a solution of 217 parts byweight of cerous nitrate in 500 parts by weight of water with stirring.The precipitate was filtered off, washed with water and dried. The drycatalyst mass was broken down to pass a 30 mesh B.S.S. sieve, mixed with2% of graphite and pelleted. The cerium to molybdenum atomic ratio inthe catalyst is 1:1.5.

A gaseous mixture of 10.1% of acrolein, 10.0% by volume of oxygen, 49.8%by volume of nitrogen, and 30. 1% by volume of steam was passed over thecatalyst maintained in a reactor at 400 C. the contact time being 4.0seconds.

Of the acrolein fed to the reactor 12.8% was converted to acrylic acid,6.1% to carbon dioxide, and 65.0% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 36.6%.

Example [6] 3 A solution of 202 parts by weight of ferric nitrate (Fe(NO.9l-1,O) in 500 parts by weight of water was mixed with a solution of132.5 parts by weight of ammonium molybdate in 500 parts by weight ofwater. A precipitate was formed, and after a few minutes the mixture setto a green gel. The well stirred mass was then dried in an oven at C.over 3 days and the solid residue sieved to pass a 30 mesh B.S.S. sieve.The powder was washed with water, dried, heated in air at 240 C. andthen formed into pellets with 2% by weight of graphite. The pellets wereheated at 600 C. for 16 hours. The iron to molybdenum atomic ratio inthe catalyst is 1:1.3.

A gaseous mixture of 9.9% by volume of acrolein, 10.1% by volume ofoxygen, 49.7% by volume of nitrogen, and 30.2% by volume of steam werepassed over the catalyst maintained in a reactor at 400 C., the contacttime being 4.0 seconds.

Of the acrolein fed to the reactor 8.7% was converted to acrylic acid,13.7% to carbon dioxide, and 38.9% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 14.2%.

Example [7'] 4 91 parts by weight of vanadium pentoxide and 144 parts byweight of molybdic oxide were intimately mixed by slurrying with water.The mixture was dried, and granulated by making into a paste with asolution of ethanolamine, and drying. The catalyst mass was broken downto 7-16 mesh size B.S.S. sieves, and the granules were heated at 550 C.for 16 hours. The vanadium to molybdenum atomic ratio in the catalyst is1:1.

A gaseous mixture of 9.8% by volume of acrolein, 10.1% by volume ofoxygen, 50.3% by volume of nitrogen, and 29.8% by volume of steam waspassed over the catalyst maintained in a reactor at 425 C., the contacttime being 4.0 seconds.

Of the acrolein fed to the reactor 28.5% was converted to acrylic acid,4.4% to carbon dioxide, and 40.5% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 47.8%.

Example [8] 5 A solution of 175 parts by weight of stannic chloride(SnCl .5l-1,O) in 500 parts by weight of water was added slowly withstirring to a solution of 177 parts by weight of ammonium molybdate in500 parts by weight of water. The precipitate formed was filtered,washed with water and dried. The solid mass was ground to pass a 30 meshB.S.S. sieve, heated at 500 C. for 16 hours, pelleted with 2% graphite,and heated at 7 50 C. for 16 hours. The tin to molybdenum atomic ratioin the catalyst is 1:2.

A gaseous mixture of 10.1% by volume of acrolein, 10.1% by volume ofoxygen, 50.3% by volume of nitrogen, and 29.5% by volume of steam waspassed over the catalyst maintained in a reactor at 370 C., the contacttime being 2.9 seconds.

of the acrolein fed to the reactor 34.2% was converted to acrylic acid,10.8% was converted to carbon dioxide, and 26.0% was recoveredunchanged.

The yield of acrylic acid based on acrolein consumed was 46.2%.

Example [9] 6 63 parts by weight of powdered tin metal were slowly addedto a well stirred solution of 379 parts by weight of nitric acid (S.G.1.42) dissolved in 1067 parts by weight of water. During addition theacid solution was maintained at its boiling point. When the addition wascomplete the mixture was boiled with stirring until no more brownnitrous fumes were evolved. The mixture was filtered, washed withdistilled water and made into a thick slurry with a little water. 3.8parts of powdered molybdic oxide were added and intimately mixed. Theresulting mixture was dried, powdered and pelleted with 2% by weight ofgraphite. The catalyst was then heat treated at 750 C. for 16 hours, andsubsequently at 1,000" C. for 16 hours. The tin to molybdenum atomicratio in the catalyst is 20:1.

A gaseous mixture of 10.1% by volume of acrolein, 10.4% by volume ofoxygen, 49.1% by volume of nitrogen and 30.4% by volume of steam waspassed over the catalyst maintained in a reactor at 400 C. the contacttime being 3.8 seconds.

Of the acrolein fed to the reactor 42.6% was converted to acrylic acid,4.9% to carbon dioxide and 29.4% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 60.4%.

Example [10] 7 63 parts by weight of powdered tin metal were slowlyadded to well stirred solution of 267 parts by volume of nitric acid(S.G. 1.42) dissolved in 1067 parts by weight of water. During theaddition the acid solution was maintained at its boiling point. When theaddition was complete the mixture was boiled with stirring until no morebrown nitrous fumes were evolved. The mixture was filtered, washed withdistilled water and made into a thick slurry with a little water. 3.8parts by weight of powdered molybdic oxide were added and mixedintimately. The resulting mixture was sucked dry on a filter and driedin an oven at C. The dry solid was powdered, mixed with 2% by weight ofgraphite and pelleted. The actalyst was then heat treated at 750" C. for16 hours and then at 1,000 C. for 16 hours. The tin to molybdenum atomicratio in the catalyst is 20: 1.

The catalyst was placed in a reactor maintained at 427 C. and a gaseousmixture of 10% by volume of propylene, 50% by volume of air and 40% byvolume of steam was passed over the catalyst, the contact time being 4seconds. Of the propylene fed 12.5% was converted to acrylic acid, 10.2%to acrolein and 5.1% to carbon dioxide. The yield of acrolein andacrylic acid based on propylene consumed was 57%.

Example [In] 8 The catalyst prepared as described in Example 10 wasplaced in a reactor maintained at 400 C. and a gaseous mixture of 10% byvolume of acrolein, 50% by volume of nitrogen, 10% by volume of oxygenand 30% by volume of steam was passed over the catalyst, the contacttime being 3.8 seconds.

Of the acrolein fed 42.6% was converted to acrylic acid and 4.9% tocarbon dioxide. The yield of acrylic acid based on acrolein consumed was60.4%.

Example [12] 9 An intimate mixture of 350 parts of antimony pentoxideand 160.6 parts of molybdenum trioxide was ground to pass a 30 meshB.S.S. sieve. 25.5 parts of graphite were added and the preparation waspelleted and subsequently heat treated at 500 C. for 23 hours. Theantimony to molybdenum atomic ratio in the catalyst is 2: 1.

A gaseous mixture of 10.1% by volume of acrolein, 49.9% by volume ofnitrogen, 10.0% by volume of oxygen, and 30.0% by volume of steam waspassed over the catalyst maintained in a reactor at 350 C. The contacttime being 4.0 seconds.

of the acrolein fed to the reactor 16.2% was converted to acrylic acid,1.6% to carbon dioxide and 61.3% was recovered unchanged.

The yield of acrylic acid based on acrolein consumed was 41.8%.

When the process was repeated at a reaction temperature of 400 C., 32.0%of the acrolein fed was converted to acrylic acid.

Example [1 3] 10 An intimate mixture of 350 parts of antimony pentoxideand 160.6 parts of molybdenum trioxide was ground to pass a 30 meshB.S.S. sieve. 25.5 parts of fine flake graphite were added, and thepreparation was pelleted and subsequently heat treated at 500 C. for 237 hours. The antimony to molybdenum atomic ratio in the catalyst is 2:1.

57.8 parts of this catalyst was placed in a conventional oxidationreactor. A mixture of 4.4% by volume of methacrolein, 44.4% by volume ofnitrogen, 5.2% by volume of oxygen and 46% by volume of steam wasintroduced into the reactor; the contact time was 4.1 seconds.

Of the methacrolein fed, 19.4mole percent was converted to methacrylicacid, and 7.4% to carbon dioxide. The yield of methacrylic acid based onmethacrolein consumed was 41.2%.

[ Example 14 I [A solution of chromium nitrate Cr(NO 9H O (400 parts byweight) dissolved in distilled water (500 parts by weight) was added toa solution of ammonium molybdate (NHJ MO O 4H O (177 parts by weight)dissolved in distilled water 1000 parts by weight of 60 C. The mixturewas brought to pH 6.6 by the addition of aqueous ammonia. The mixturewas filtered and the solid washed once by resuspension for 15 minutes indistilled water 1000 parts by weight), and filtered. The cake was driedat l 10 C. for 16 hours, broken down to pass 30 mesh (B.S.S.), mixedwith graphite (1% by weight), pelleted and heated in air in a mufflefurnace. The furnace temperature was programmed from 200 C. to 700 C. at22 C. per hour and maintained at 700 C. for 16 hours. The chromium tomolybdenum ratio is A gaseous mixture of 7% by volume of acrolein, byvolume of oxygen, 58% by volume of nitrogen and 30% by volume of steamwas passed over the catalyst in a reactor maintained at 390 C., thecontact time being 3 seconds.

Of the total acrolein fed to the reactor, 42% was converted to acrylicacid, 24% to carbon oxides and 27% was recovered unchanged] What isclaimed is:

l. A process which comprises reacting in vapor phase at about 300500 C.an aldehyde selected from the group consisting of acrolein andmethacrolein to produce the corresponding acid with molecular oxygenover an oxidation catalyst consisting essentially of l a mixture of anoxide of molybdenum and an oxide of a polyvalent metal selected from thegroup consisting of the oxides of vanadium, iron, cerium, titanium,]antimony, tin, and tungsten [and bismuth] or (2) a compound ofmolybdenum, oxygen and said polyvalent metal; the atomic ratio ofpolyvalent metal to molybde num being from 20:1 to 1:65; the percentageof feed substance in the reactant feed being from 1 to 20% by volume,the reactant feed containing from 1 to 20% by volume of oxygen, and thecontact time being from 1 to 30 seconds.

2. A process as claimed in claim I wherein the catalyst consists ofantimony molybdate.

3. A process as claimed in claim 1 wherein the catalyst consists of tinmolybdate.

4. A process as claimed in claim 1 employing a supported catalyst.

5. A process as claimed in claim 4 wherein the catalyst is supported onalumina.

6. A process as claimed in claim 4 wherein the catalyst is supported onsilica.

7. A process as claimed in claim 1 wherein the reactant feed containsbetween about 2 and 10% by volume of feed substance.

8. A process as claimed in claim 1 wherein the reactant feed containsbetween 2 and 15% by volume of molecular oxygen.

9. A process as claimed in claim 1 wherein the molecular oxygen issupplied in the form of air.

10. A process as claimed in claim 1 carried out in the presence of aninert diluent selected from the group consisting of nitrogen, propane,butane, isobutane, carbon dioxide, steam and mixtures thereof.

11. A process as claimed in claim 10 wherein the proportion of steam asinert diluent is between 2 and 60% by volume of the reactant feed.

12. A process as claimed in claim 10 wherein the inert diluent isnitrogen.

13. A process as claimed in claim 10 wherein the inert diluent is amixture of steam and nitrogen.

14. A process which comprises reacting in vapor phase at about 300500 C.an aldehyde selected from the group consisting of acrolein andmethacrolein to produce the corresponding acid with molecular oxygenover an oxidation catalyst consisting essentially of(l) a mixture of anoxide of molybdenum and an oxide of tungsten or (2) a compound ofmolybdenum, oxygen and tungsten; the atomic ratio of tungsten tomolybdenum being from 20:] to 1:65; the percentage offeed substance inthe reactantfeed beingfrom I to 20% by volume, the reactant feedcontainingfrom l to 20% by volume ofoxygen, and the contact time beingfrom I to 30 seconds.

15 A process which comprises reacting in vapor phase at about 300-500 C.an aldehyde selected from the group consisting of acrolein andmethacrolein to produce the corresponding acid with molecular oxygenover an oxidation catalyst consisting essentially of (I) a mixture ofanoxide ofmolybdenum and an oxide ofcerium or (2) a compound ofmolybdenum, oxygen and cerium; the atomic ratio of cerium to molybdenumbeing from 20:] to l :65 the percentage of feed substance in thereactant feed being from I to 20% by volume, the reactant feedcontaining from I to 20% by volume ofoxygen, and the contact time beingfrom 1 to 30 seconds.

16. A process which comprises reacting in vapor phase at about 300500 C.an aldehyde selected from the group consisting of acrolein andmethacrolein to produce the corresponding acid with molecular oxygenover an oxidation catalyst consisting essentially of(l) a mixture ofanoxide ofmolybdenum and an oxide ofvanadium or (2) a compoundofmolybdenum, oxygen and vanadium; the atomic ratio of vanadium tomolybdenum beingfrom 20:1 to 1:65; the percentage of feed substance inthe reactant feed being from I to 20% by volume, the reactant feedcontaining from I to 20% by volume ofoxygen, and the contact time beingfrom I to 30 seconds.

1 7. A process which comprises reacting in vapor phase at about 300500C. an aldehyde selected from the group consisting of acrolein andmethacrolein to produce the corresponding acid with molecular oxygenover an oxidation catalyst consisting essentially of(l) a mixture ofanoxide of molybdenum and an oxide of iron or (2) a compound ofmolybdenum, oxygen and iron; the atomic ratio ofiron to molybdenum beingfrom 20:1 to 1:65; the percentage of feed substance in the reactant feedbeing from I to 20% by volume, the reactant feed containing from I to20% by volume ofoxygen, and the contact time being from I to 30 seconds.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. RE 23593 DATED 1 October 28, 1975 INVENTOR(S) JAMES ROBERT BETHELL ET AL Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 1, line 65 "molybdate" should read -molybdates- Col. 5, lime 5OAfter "During insert --the- Col. 6, line 18 "actalyst" should read--catalyst line 31 "Example 10" should read -Example 7-- Col. 8, line 14"2" should read -20- (Claim 11) Signed and Scaled this third Day OfFebruary 1976 [SEAL] Arrest:

RUTH c. MASON c. MARSHALL DANN Arresting Officer Commissioner uj'Parenrsand Trademarks

1. A PROCESS WHICH COMPRISES REACTING IN VAPOR PHASE AT ABOUT 300*-500*C. AN ALDEHYDE SELECTED FROM THE GROUP CONSISTING OF ACROLEIN ANDMETHACROLEIN TO PRODUCE THE CORRESPONDING ACID WITH MOLECULAR OXYGENOVER AN OXIDATION CATALYST CONSISTING ESSENTIALLY OF (1) A MIXTURE OF ANOXIDE OF MOLYBDENUM AND AN OXIDE OF A POLYVALENT METAL SELECTED FROM THEGROUP CONSISTING OF THE OXIDES OF VANADIUM, IRON, CERIUM, (TITANIUM,)ANTIMONY, TIN, AND TUNGSTEN (AND BISMUTH) OR (2) A COMPOUND OFMOLYBDENUM, OXYGEN AND SAID POLYVALENT METAL, THE ATOMIC RATIO OFPOLYVALINT METAL TO MOLYBDENUM BEING FROM 20:1 TO 1:65, THE PERCENTAGEOF FEED SUBSTANCE IN THE REACTANT FEED BEING FROM 1 TO 20% BY VOLUME,THE REACTANT FEED CONTAINING FROM 1 TO 20% BY VOLUME OF OXYGEN, AND THECONTACT TIME FROM 1 TO 30 SECONDS.
 2. A process as claimed in claim 1wherein the catalyst consists of antimony molybdate.
 3. A process asclaimed in claim 1 wherein the catalyst consists of tin molybdate.
 4. Aprocess as claimed in claim 1 employing a supported catalyst.
 5. Aprocess as claimed in claim 4 wherein the catalyst is supported onalumina.
 6. A process as claimed in claim 4 wherein the catalyst issupported on silica.
 7. A process as claimed in claim 1 wherein thereactant feed contains between about 2 and 10% by volume of feedsubstance.
 8. A process as claimed in claim 1 wherein the reactant feedcontains between 2 and 15% by volume of molecular oxygen.
 9. A processas claimed in claim 1 wherein the molecular oxygen is supplied in theform of air.
 10. A process as claimed in claim 1 carried out in thepresence of an inert diluent selected from the group consisting ofnitrogen, propane, butane, isobutane, carbon dioxide, steam and mixturesthereof.
 11. A process as claimed in claim 10 wherein the proportion ofsteam as inert diluent is between 2 and 60% by volume of the reactantfeed.
 12. A process as claimed in claim 10 wherein the inert diluent isnitrogen.
 13. A process as claimed in claim 10 wherein the inert diluentis a mixture of steam and nitrogen.
 14. A process which comprisesreacting in vapor phase at about 300*-500* C. an aldehyde selected fromthe group consisting of acrolein and methacrolein to produce thecorresponding acid with molecular oxygen over an oxidation catalystconsisting essentially of (1) a mixture of an oxide of molybdenum and anoxide of tungsten or (2) a compound of molybdenum, oxygen and tungsten;the atomic ratio of tungsten to molybdenum being from 20:1 to 1:65; thepercentage of feed substance in the reactant feed being from 1 to 20% byvolume, the reactant feed containing from 1 to 20% by volume of oxygen,and the contact time being from 1 to 30 seconds.
 15. A process whichcomprises reacting in vapor phase at about 300*-500* C. an aldehydeselected from the group consisting of acrolein and methacrolein toproduce the corresponding acid with molecular oxygen over an oxidationcatalyst consisting essentially of (1) a mixture of an oxide ofmolybdenum and an oxide of cerium or (2) a compound of molybdenum,oxygen and cerium; the atomic ratio of cerium to molybdenum being from20:1 to 1:65; the percentage of feed substance in the reactant feedbeing from 1 to 20% by volume, the reactant feed containing from 1 to20% by volume of oxygen, and the contact time being from 1 to 30seconds.
 16. A process which comprises reacting in vapor phase at about300*-500* C. an aldehyde selected from the group consisting of acroleinand methacrolein to produce the corresponding acid with molecular oxygenover an oxidation catalyst consisting essentially of (1) a mixture of anoxIde of molybdenum and an oxide of vanadium or (2) a compound ofmolybdenum, oxygen and vanadium; the atomic ratio of vanadium tomolybdenum being from 20:1 to 1:65; the percentage of feed substance inthe reactant feed being from 1 to 20% by volume, the reactant feedcontaining from 1 to 20% by volume of oxygen, and the contact time beingfrom 1 to 30 seconds.
 17. A process which comprises reacting in vaporphase at about 300*-500* C. an aldehyde selected from the groupconsisting of acrolein and methacrolein to produce the correspondingacid with molecular oxygen over an oxidation catalyst consistingessentially of (1) a mixture of an oxide of molybdenum and an oxide ofiron or (2) a compound of molybdenum, oxygen and iron; the atomic ratioof iron to molybdenum being from 20:1 to 1:65; the percentage of feedsubstance in the reactant feed being from 1 to 20% by volume, thereactant feed containing from 1 to 20% by volume of oxygen, and thecontact time being from 1 to 30 seconds.